UVA generated free radicals in irinotecan (CPT-11) in the presence of copper ions

Irinotecan (CPT-11) is an efficient anticancer drug approved for clinical use in the treatment of advanced colorectal cancers. This work is focused on the study of photoinduced processes in irinotecan (CPT-11) both in the presence and absence of Cu(II) ions by means of UV/vis and EPR spectroscopy. Solid-state EPR revealed the solvent dependent coordination between CPT-11 and cupric ions. EPR spin trapping technique, using various spin trapping agents, was applied to monitor the generation of reactive radical species (oxygen- and carbon-centered radicals) in irradiated CPT-11 and CPT-11/CuCl2 systems under the given experimental conditions. We confirmed that the presence of CPT-11 is necessary for the formation of reactive radicals and the photoinduced processes are influenced by the presence of cupric ions. ROS generated upon irradiation of CPT-11 in the presence/absence of copper ions can be regarded as complementary species to the original inhibitory action of the drug on the DNA topoisomerase I.